SPDL1 and central nervous system cancer: The median sPD-L1 concentration in sPD-L1-positive samples at baseline was 0.321 ng/ml (range: 0.080–42.110 ng/ml) in patients with GBM and 0.658 ng/ml (range: 0.060–2.250 ng/ml) in patients with WHO grade II–III glioma (p = 0.465, Mann–Whitney U test; Supplementary Fig. 1A).